The political terms "Left" and "Right" were coined during the French Revolution (1789–1799), referring to the seating arrangement in the French Estates General: those who sat on the left generally opposed the monarchy and supported the revolution, including the creation of a republic and secularization,[6] while those on the right were supportive of the traditional institutions of the Old Regime. Use of the term "Left" became more prominent after the restoration of the French monarchy in 1815 when it was applied to the "Independents".[7] The word "wing" was appended to Left and Right in the late 19th century, usually with disparaging intent and "left-wing" was applied to those who were unorthodox in their religious or political views.

Since the Right was populist, both in the Western and the Eastern Bloc anything viewed as avant-garde art was called leftist in all Europe, thus the identification of Picasso's Guernica as "leftist" in Europe[25][page needed] and the condemnation of the Russian composer Shostakovich's opera (The Lady Macbeth of Mtsensk District) in Pravda as follows: "Here we have 'leftist' confusion instead of natural, human music".[26][page needed]

Other leftists believe in Marxian economics, which are based on the economic theories of Karl Marx. Some distinguish Marx's economic theories from his political philosophy, arguing that Marx's approach to understanding the economy is independent of his advocacy of revolutionary socialism or his belief in the inevitability of proletarian revolution.[29][30] Marxian economics does not exclusively rely upon Marx, but it draws from a range of Marxist and non-Marxist sources. The "dictatorship of the proletariat" or "workers' state" are terms used by some Marxists, particularly Leninists and Marxist–Leninists, to describe what they see as a temporary state between the capitalist state of affairs and a communist society. Marx defined the proletariat as salaried workers, in contrast to the "Lumpenproletariat", who he defined as outcasts of society, such as beggars, tricksters, entertainers, buskers, criminals and prostitutes.[31] The political relevance of farmers has divided the left. In Das Kapital, Marx scarcely mentioned the subject.[32]Mao Zedong believed that it would be rural peasants, not urban workers, who would bring about the proletarian revolution.

One of the foremost left-wing advocates was Thomas Paine, one of the first individuals since left and right became political terms to describe the collective human ownership of the world which he speaks of in Agrarian Justice.[36] As such, must of left-wing thought concerning environmentalism stems from this duty of ownership, and this cooperative ownership means that we need to take care of it. This is reflected in much of the historical left-wing thought that came after, although there were disagreements about what this entailed.

Both Karl Marx and the early socialist William Morris arguably had a concern for environmental matters.[37][38][39][40] According to Marx: "Even an entire society, a nation, or all simultaneously existing societies taken together [...] are not owners of the earth. They are simply its possessors, its beneficiaries, and have to bequeath it in an improved state to succeeding generations".[37][41] Following the Russian Revolution, environmental scientists such as revolutionary Alexander Bogdanov and the Proletkult organisation made efforts to incorporate environmentalism into Bolshevism and "integrate production with natural laws and limits" in the first decade of Soviet rule, before Joseph Stalin attacked ecologists and the science of ecology, purged environmentalists and promoted the pseudo-science of Trofim Lysenko.[42][43][44] Likewise, Mao Zedong rejected environmentalism and believed that based on the laws of historical materialism all of nature must be put into the service of revolution.[45]

From the 1970s onwards, environmentalism became an increasing concern of the left, with social movements and some unions campaigning over environmental issues. For example, the left-wing Builders Labourers Federation in Australia, led by the communist Jack Mundy, united with environmentalists to place green bans on environmentally destructive development projects.[46] Some segments of the socialist and Marxist left consciously merged environmentalism and anti-capitalism into an eco-socialist ideology.[47]Barry Commoner articulated a left-wing response to The Limits to Growth model that predicted catastrophic resource depletion and spurred environmentalism, postulating that capitalist technologies were chiefly responsible for environmental degradation, as opposed to population pressures.[48] Environmental degradation can be seen as a class or equity issue, as environmental destruction disproportionately affects poorer communities and countries.[49]

Several left-wing or socialist groupings have an overt environmental concern and several green parties contain a strong socialist presence. For example, the Green Party of England and Wales features an eco-socialist group, Green Left, that was founded in June 2005. Its members held some influential positions within the party, including both the former Principal Speakers Siân Berry and Dr. Derek Wall, himself an eco-socialist and Marxist academic.[50] In Europe, some Green left political parties combine traditional social-democratic values such as a desire for greater economic equality and workers rights with demands for environmental protection, such as the Nordic Green Left.

In the 21st century, questions about the environment have become increasingly politicized, with the Left generally accepting the findings of environmental scientists about global warming[58][59] and many on the Right disputing or rejecting those findings.[60][61][62] However, the left is divided over how to effectively and equitably reduce carbon emissions: the center-left often advocates a reliance on market measures such as emissions trading or a carbon tax, while those further to the left tend to support direct government regulation and intervention either alongside or instead of market mechanisms.[63][64][65]

The question of nationality and nationalism has been a central feature of political debates on the Left. During the French Revolution, nationalism was a policy of the Republican Left.[66] The Republican Left advocated civic nationalism[6] and argued that the nation is a "daily plebiscite" formed by the subjective "will to live together". Related to "revanchism", the belligerent will to take revenge against Germany and retake control of Alsace-Lorraine, nationalism was sometimes opposed to imperialism. In the 1880s, there was a debate between those, such as Georges Clemenceau (Radical), Jean Jaurès (Socialist) and Maurice Barrès (nationalist), who argued that colonialism diverted France from the "blue line of the Vosges" (referring to Alsace-Lorraine); and the "colonial lobby", such as Jules Ferry (moderate republican), Léon Gambetta (republican) and Eugène Etienne, the president of the parliamentary colonial group. After the Dreyfus Affair, nationalism instead became increasingly associated with the far-right.[67]

The failure of revolutions in Germany and Hungary ended Bolshevik hopes for an imminent world revolution and led to promotion of "Socialism in One Country" by Joseph Stalin. In the first edition of the book Osnovy Leninizma (Foundations of Leninism, 1924), Stalin argued that revolution in one country is insufficient, but by the end of that year in the second edition of the book he argued that the "proletariat can and must build the socialist society in one country". In April 1925, Nikolai Bukharin elaborated the issue in his brochure Can We Build Socialism in One Country in the Absence of the Victory of the West-European Proletariat?, whose position was adopted as state policy after Stalin's January 1926 article On the Issues of Leninism (К вопросам ленинизма). This idea was opposed by Leon Trotsky and his followers who declared the need for an international "permanent revolution". Various Fourth Internationalist groups around the world who describe themselves as Trotskyist see themselves as standing in this tradition, while Maoist China supported Socialism in One Country.

European social democrats strongly support Europeanism and supranational integration, although there is a minority of nationalists and eurosceptics also in the left. Some link this left-wing nationalism to the pressure generated by economic integration with other countries encouraged by free trade agreements. This view is sometimes used to justify hostility towards supranational organizations. Left-wing nationalism can also refer to any nationalism which emphasises a working-class populist agenda which seeks to overcome perceived exploitation or oppression by other nations. Many Third World anti-colonial movements adopted left-wing and socialist ideas.

Other left-wing religious movements include Islamic socialism and Buddhist socialism. There have been alliances between the left and anti-war Muslims, such as the Respect Party and the Stop the War Coalition in Britain. In France, the left has been divided over moves to ban the hijab from schools, with some supporting a ban based on separation of church and state and others opposing the prohibition based on personal freedom.

Various counterculture movements in the 1960s and 1970s were associated with the "New Left". Unlike the earlier leftist focus on union activism, the New Left instead adopted a broader definition of political activism commonly called social activism. The New Left in the United States is associated with the hippie movement, college campus mass protest movements, and a broadening of focus from protesting class-based oppression to include issues such as gender, race and sexual orientation. The British New Left was an intellectually driven movement which attempted to correct the perceived errors of "Old Left".

The New Left opposed prevailing authority structures in society, which it termed "The Establishment" and became known as "anti-Establishment". The New Left did not seek to recruit industrial workers but rather concentrated on a social activist approach to organization, convinced that they could be the source for a better kind of social revolution. This view has been criticised by some Marxists (especially Trotskyists) who characterized this approach as "substitutionism", which they described as a misguided and non-Marxist belief that other groups in society could "substitute" for the revolutionary agency of the working class.[78][79]

Leftist postmodernism opposes attempts to supply universal explanatory theories, including Marxism, deriding them as grand narratives. It views culture as a contested space and via deconstruction seeks to undermine all pretensions to absolute truth. Left-wing critics of post-modernism assert that cultural studies inflates the importance of culture by denying the existence of an independent reality.[93][94]

^Maass, Alan; Zinn, Howard (2010). The Case for Socialism (Revised ed.). Haymarket Books. p. 164. ISBN978-1608460731. The International Socialist Review is one of the best left-wing journals around...

^Schmidt, Michael; Van der Walt, Lucien (2009). Black Flame: The Revolutionary Class Politics of Anarchism and Syndicalism. Counter-Power. 1. AK Press. p. 128. ISBN978-1-904859-16-1. [...] anarchism is a coherent intellectual and political current dating back to the 1860s and the First International, and part of the labour and left tradition

^Revel, Jean Francois (2009). Last Exit to Utopia. Encounter Books. p. 24. ISBN978-1594032646. In the United States, the word liberal is often used to describe the left wing of the Democratic party.

^Barry, John (2002). International Encyclopedia of Environmental Politics. Taylor & Francis. ISBN978-0415202855. All surveys confirm that environmental concern is associated with green voting...[I]n subsequent European elections, green voters have tended to be more left-leaning...the party is capable of motivating its core supporters as well as other environmentally minded voters of predominantly left-wing persuasion...

^Arnold, N. Scott (2009). Imposing values: an essay on liberalism and regulation. Florence: Oxford University Press. p. 3. ISBN978-0-495-50112-1. Modern liberalism occupies the left-of-center in the traditional political spectrum and is represented by the Democratic Party in the United States, the Labor Party in the United Kingdom, and the mainstream Left (including some nominally socialist parties) in other advanced democratic societies.

^Andrew C. Revkinnov (13 November 2007). "Global Warming – Books – The New York Times". New York Times. Retrieved 15 November 2016. Challenges to both Left and Right on Global Warming", by Andrew C. Revkin, Nov. 13, 2007, "The right says global warming is somewhere between a hoax and a minor irritant, and argues that liberals' thirst for top-down regulations will drive American wealth to developing countries and turn off the fossil-fuelled engine powering the economy.

^Mooney, Chris (2006). The Republican War on Science (Rev ed.). New York: BasicBooks. pp. 4–5. ISBN978-0-465-04676-8. [T]he modern Right has adopted a style of politics that puts its adherents in increasingly stark conflict with both scientific information and dispassionate, expert analysis in general.

^Doyle, William (2002). The Oxford History of the French Revolution (2nd ed.). Oxford: Oxford University Press. ISBN978-0-19-925298-5. An exuberant, uncompromising nationalism lay behind France's revolutionary expansion in the 1790s...", "The message of the French Revolution was that the people are sovereign; and in the two centuries since it was first proclaimed it has conquered the world.